Autopilot automatic disconnect system for fly-by-wire aircraft

Abstract

A system for backdriving the flight deck controllers of a fly-by-wire aircraft that is under autopilot control to provide a pilot with tactile and visual feedback of autopilot activity. The system, distributed between the aircraft primary flight computers and the autopilot flight computer, uses actuators mechanically coupled to each flight deck controller to position the flight deck controller to mimic manual operation of the flight control surfaces. Additionally, the system allows smooth disengagement of the autopilot and transfer of the aircraft to pilot control when the pilot takes control of any flight deck controller by moving it from a backdrive system-commanded position by a predetermined displacement for a predetermined time.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
       1. An autopilot automatic disconnect system of an aircraft having a fly-by-wire control system, the disconnect system comprising: (a) predicting a position of a flight deck controller;   (b) sensing an actual position of the flight deck controller;   (c) comparing the predicted position and the actual position of the flight deck controller to determine a difference in the positions;   (d) comparing the difference with a predetermined threshold value; and   (e) disengaging the autopilot when the difference signal exceeds the threshold value for a period of time, the time dependent upon the magnitude of the difference between the actual position of the flight deck controller and the predicted position of said controller.   
     
     
       2. The disconnect system of claim 1, wherein the flight deck controller is a column controller for controlling aircraft pitch, and the predicting of step (a) comprises: converting an autopilot pitch command to an equivalent column position; and   limiting the equivalent column position with input signals representative of impact pressure related to aircraft velocity.   
     
     
       3. The disconnect system of claim 2, wherein the limiting step comprises: mimicking a variable-feel force that a pilot would experience when the pilot is operating the column controller under conditions of manual pilot control of the aircraft.   
     
     
       4. The disconnect system of claim 3, wherein the step of limiting comprises: setting different limits to distinguish between a limit during aircraft cruise and aircraft autoland conditions.   
     
     
       5. The disconnect system of claim 2, wherein the step of predicting further comprises; filtering a backdrive command signal to eliminate noise;   applying a gain factor relating to aircraft speed to the filtered command,; and   delaying the gain factor-applied backdrive command signal to produce a predicted position of the flight deck controller.   
     
     
       6. The disconnect system of claim 2, wherein the step of comparing the difference comprises: converting the difference between the predicted and actual position of the flight deck controller to a signal proportional to g-forces; and   varying the predetermined threshold value in proportion to flight speed of the aircraft.   
     
     
       7. The disconnect system of claim 1, wherein the prediction of the position of a flight deck controller comprises predicting the position of a controller selected from a wheel flight deck controller and a pedal flight deck controller. 
     
     
       8. An autopilot automatic disconnect system of an aircraft having a fly-by-wire control system, the disconnect system comprising: (a) predicting a position of a flight deck controller by: filtering a back drive command signal to eliminate noise, applying a gain factor relating to aircraft speed to the filtered command, and delaying the gain factor-applied back drive command signal to produce a predicted position of the flight deck controller;   (b) sensing an actual position of the flight deck controller;   (c) comparing the predicted position and the actual position of the flight deck controller to determine a difference in the positions;   (d) comparing the difference with a predetermined threshold value; and   (e) disengaging the autopilot when the difference exceeds the threshold value.   
     
     
       9. An autopilot automatic disconnect system of an aircraft having a fly-by-wire control system, the disconnect system comprising: (a) predicting a position of a flight deck controller;   (b) sensing an actual position of the flight deck controller;   (c) comparing the predicted position and the actual position of the flight deck controller to determine a difference in the positions;   (d) comparing the difference with a predetermined threshold value, said comparing including converting the difference between the prediced and actual postion of the flight deck controller to a signal proportional to g-forces; and   (e) disengaging the autopilot when the difference exceeds the threshold value.